The present invention relates to a recording apparatus for recording characters, for example, on a recording medium by utilizing liquid ink. More particularly, the invention relates to a recording apparatus of which an ink tank alone can be replaced with another, and an ink tank used for the recording apparatus.
A recording apparatus (referred to simply as a printer) with an ink tank detachably attached thereto, and an ink tank are disclosed in the Unexamined Japanese Patent Application Publication No. Hei. 6-255121. In the publication, an ink holding member, which is disposed in an ink tank, holds ink therein. When the ink tank is attached to the printer, an ink introducing port of a recording head (referred to as a print head) is brought into contact with the ink holding member.
Usually, an urethanes material is used for making the ink holding member 3a. A recent market demands the improvement of a print quality (waterproofness of print). With the demand, ink tends to take an increase of its pH value. A demand for the development of the ink holding member formed of felt as a material resistive to a high pH ink is also increasing. Also in the publication, the felt is used for making the ink holding member in order to increase its capabilities of ink holding and ink supplying.
In the construction of the publication, the ink introducing port of the print head directly pushes the ink holding member. Therefore, if the attaching and detaching of the ink tank to and from the print head are repeated, the ink holding member will be deformed, and a rate of used ink to ink contained in the ink tank (referred to as an ink use rate) will be decreased. Particularly when the felt is used for the ink holding member, the decrease of the ink use rate is remarkable. The reason for this follows. To manufacture ink tanks of the same size, the ink holding member, when felt is used, must be formed at a lower pressure than when urethanes is used. Therefore, a reaction force of the ink holding member formed of felt is weak, a posture variation of the ink holding member is great, and the ink holding member is hart to resume its original posture.
A solution to the problem is proposed in the Unexamined Japanese Patent Application Publication No. Hei. 7-148938. In the publication, the ink passing member is directly jointed to the ink holding member within the ink tank. When the ink tank is attached to the print head or the printer, the ink introducing port of the print head is pressed against the ink passing member, to thereby form a passage of ink. With the structure, the ink holding member is not deformed by the attaching and detaching of the ink tank. Therefore, the problem as mentioned above does not arise.
In the structure where the ink passing member is press fit to the ink holding member, the ink holding member is deformed in the jointing portion where the ink holding member is coupled with the ink passing member. Because of this, a gap is formed between the ink holding member and the wall surface of the ink tank. Air staying there enters the jointing portion to possibly close the ink passage. The ink held by the ink holding member is not fully used.
As shown in FIG. 1C in the Japanese Patent Application No. Hei. 7-268752, a unique ink tank is constructed such that the meniscus forming member having a plural number of minute perforations is brought into contact or press contact with the ink holding member. In the ink tank thus constructed, it is possible to improve a degree of the contact of the inner wall of the ink tank with the ink holding member. Therefore, the entering of air bubbles into the ink tank can be reduced to an extreme. If air enters the ink tank, it is trapped with the surface of the meniscus forming member to allow little air to enter the inside of the print head. In the ink tank of the publication, material of felt may be used for making the ink holding member, in addition to the materials of urethanes.
The ink tank under discussion suffers from the following problem, however. When the ink tank is attached to the printer, air stays in a space between the meniscus forming member and the ink introducing port of the print head. Such air can insufficiently be removed if it is sucked from the nozzle side in its maintenance. This causes a printing problem.
Another jointing structure is disclosed in the Unexamined Japanese Patent Application Publication No. Hei. 6-272745. In the structure, a porous member of which the volume is variable is provided at the jointing portion between the ink tank and the print head. When the ink tank is detached, and the porous member expands in its volume, the porous member absorbs an amount of air corresponding to the expanded volume of the porous member. This leads to the printing problem.
Further, the present invention relates to a printer having a print head for printing characters, for example, on a printing medium by ejecting ink droplets to the printing medium, and an ink tank which holds ink therein to be supplied to the print head and is detachably connectable with the print head, and an ink tank used for the printer. More particularly, the invention relates to a jointing structure for jointing the ink tank to tho print head when the ink tank is attached to the print head.
The ink jet printer is widely used because of its many advantageous features, for example, high quality print picture, low noise generation, and the like. Particularly, its size may be reduced in design. Because of this feature, most of the ink jet printers currently marketed are provided for personal use. In handling small printers for personal use, when ink is used up, the user replaces an old ink jet cartridge with a new one. The cartridge is formed integral with an ink tank or a print head. Particularly where only the ink tank is replaced, the replacement entails no increase of cost since the ink tank is relatively inexpensive, and hence the reduction of running cost of the printer.
The printer of this type in which the ink tank is replaced for supplying ink to the printer suffers from the following problem. When the ink tank is replaced with a new one, ink oozes out in the jointing portion of the ink tank, and sometimes the oozed ink soils the hand of a user or drips onto the printer body.
A technique to solve this problem is disclosed in the Unexamined Japanese Patent Application Publication No. Hei. 3-92356. In the technique, an ink supplying port located at the lower side of the ink tank is constructed with a rubber plug. The rubber plug is pierced with an ink supplying needle made of metal, so that the ink tank is communicatively connected to an ink passage destined to the print head. The ink supplying needle used is resistive to corrosion by ink, and its tip is extremely sharp so that it can easily pierce the rubber plug. When the ink tank is detached from the print head, the ink supplying port of the ink tank closes by an elasticity of the rubber plug. Therefore, no ink leaks from the ink tank. When the ink tank is detached from the printer, the user mistakenly touches the sharp tip of the ink supplying needle and is injured by the sharpened tip. The inside diameter of the ink supplying needle is small. Therefore, when the rubber plug is broken with the needle and broken pieces of the rubber plug produced enters the through hole of the needle, the needle will be clogged with the broken piece.
Another technique to solve the problem is disclosed in the Unexamined Japanese Patent Application Publication No. Sho. 50-74341. The technique is based on such a jointing structure as to allow a liquid introducing pipe whose tip is not so sharp to pass therethrough. In the jointing structure, a cover plate with perforations, made of rubber, for example, is placed at the end of the ink supplying port. The perforations of the cover plate are sealed with a thin film with slits, made of rubber, for example. Also in the jointing structure, a slight amount of ink leaks through the perforations and the slits.
A further technique is disclosed in the Unexamined Japanese Patent Application Publications Nos. Hei. 2-214665 or Hei 6-966. The following jointing structure is employed in the solution. In the means, a jointing portion of the ink tank is sealed with a sealing member. A jointing portion of the printer is constructed with a porous rigid member having boring protrusions formed on the periphery thereof. To attach the ink tank to the printer, the sealing member of the ink tank is bored with the boring protrusions of the porous rigid member, and the porous rigid member of the ink tank is pressed against the porous member in the ink tank. The tip of the ink supplying pipe with the porous rigid member is wide enough to prevent the pipe from being clogged with a broken piece of the sealing member. The boring protrusions of the porous rigid member may be not so sharp. Therefore, there is less chance that an operator is injured by the protrusions. In an initial state, the jointing portion is sealed with the sealing member, so that no ink leaks from the ink tank. In the jointing structure, the porous rigid member is always impregnated with ink. Therefore, when the ink tank is attached to and detached from the printer, supplied ink drips.
Various color printers have been developed and marketed. In the color printer, a unit type print head capable of printing, for example, characters of a plural number of colors comes into use. In the unit type print head, leaked or dripping ink leads to a mixture of different colors of inks.
A jointing structure to eliminate the leakage or dripping of ink is proposed in tho Unexamined Japanese Patent Application Publication No. Hei. 6-272747. In the structure, a porous member is provided at the jointing portion of the ink tank. The volume of the porous member when the ink tank is attached is different from that when the ink tank is detached. When the ink tank is detached from the printer, the porous member expands to absorb ink. Then, there is less chance of dripping ink. When the porous member expands, it absorbs air, together with ink. When the ink tank is attached to the printer, air absorbed by the porous member is left in the ink passage. The left air possibly leads to print defects.
A pressure contact sometimes ensues an instable ink supply. A technique is known in which the extended pipe is pressed against the capillary member to increase a density of the capillary pipe to thereby supply ink, as described in (d) in claim 11 of U.S. Pat. No. 4,771,295, for example. In the technique, when the pressing force is small, the density of the capillary member is small. In this state, in supplying ink, air is sucked together with ink. Conversely, when the pressing force is large, the density of the capillary member is too large, to adversely affect the ink supply. The jointing structure in which the expanded pipe is pressed against the capillary member, the characteristic of the printer depends easily on a quantity of press contact. The manufactured products are not uniform in characteristics. Therefore, the printer based on this jointing structure frequently suffers from print defects.